tolong kak di bantu pake cara ya

a = BC = 9
b = AC = 7
c = AB = 8

Teorema cosinus
cosA = (AB^2 + AC^2 - BC^2)/2AB×AC
cosA = (8^2 + 7^2 - 9^2) / 2.8.7
cosA = (64 + 49 - 81) / 2.8.7
cosA = 32 / 2.8.7
cosA = 2/7

sinA = (akar(7^2 - 2^2))/7 --> teorema phytagoras
sinA = (akar(49-4))/7
sinA = (akar45)/7
sinA = 3/7 akar5 (E)

smg membantu

a^2 = b^2 + c^2 -2bc cos A
9^2 = 7^2 + 8^2 - 2.7.8 cos A
81 = 49 + 64 -112 cos A
112 cos A = 113 - 81
112 cos A = 32
cos A = 32/112
cos A = 2/7
sin^2 A = 1 - cos^2A
sin^2A = 1 - (2/7)^2
sin^2A = 1 - 4/49
sin^2A = 45/49
sin A = √(45/49)
sin A = (3/7)√5